I recently attended as a part of the ongoing Excitera Mobile Cup series in Sweden an event hosted by the Green hat People company. Green hat People does event sevices for mobile phones. Niklas Tyllström, the founder presented the company and organized us into competing groups of users for the event game. You can custom make your own trivia game related to whatever event you are doing or sponsoring as a part of, e.g. a tradeshow. Since we were all in the same office building, there were no location based trivia questions. The game console application monitors all the participants, time, answers and can award users.
I like this service, I think this can be perfectly used for all kinds of events, promotions, games, awards, award points, polls and so on. Head over to the website http://www.greenhatpeople.com/ to read more about them.